Electromagnetic production ofΣhypernuclei

The formation of sigmas through low-energy kaon photoproduction from nucleons is described by using Feynman diagrams. Different models for the production process are compared, including pseudovector versus pseudoscalar coupling for the KNΣ vertex. The elementary coupling constants are fitted to the cross-section data up to 2.2 GeV and agree with previous fits obtained from the photoproduction of lambdas from protons. This operator is then implanted into the nucleus via the impulse approximation. Using Woods-Saxon shell-model wave functions for the sigma and the nucleon and a particle-hole basis for the nucleus, angular distributions are obtained for the formation of ${}_{{}_{\mathrm{\Sigma }}{}^{16}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{N}$, ${}_{{}_{\mathrm{\Sigma }}{}^{40}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{K}$, and ${}_{{}_{\mathrm{\Sigma }}{}^{208}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{Tl}$. Cross sections for processes employing the reaction ${}_{}{}^1{}_{}{}^{}\mathrm{H}$(γ,$K^{+}$)${\Sigma }^0$ are about one fifth of those corresponding to lambda hypernuclei, while reactions involving n(γ,$K^{+}$)${\Sigma }^{\mathrm{-}}$ yield counting rates comparable to those of lambda-hypernuclear photoproduction.